I've just spent a frustrating couple of hours struggling to get FLAG_JSLENGTH to work, eventually discovering that it doesn't work if FLAG_METHOD is also set. Fortunately, in my case I didn't actually need FLAG_METHOD - I had only set it as I was exploring LightNCandy's capabilities and forgot to remove it. However, it is an undocumented limitation, so I wanted to post it here in case it can be fixed/documented or someone else runs into the same issue.